Olefin recovery in an olefin production process

ABSTRACT

Disclosed is a method for recovering olefin in an oxygenate to olefin production process. The method includes reacting a stream containing olefin with water in the presence of a hydrating catalyst to produce an alcohol containing stream. The alcohol containing stream can be used as an oxygenate feed in the oxygenate to olefin production process.

FIELD OF INVENTION

This invention relates to recovering olefin from an olefin productionprocess. In particular this invention relates to recovering lightolefin, such as ethylene or propylene, from an olefin productionprocess, converting the olefin to alcohol, and converting the alcohol toolefin.

BACKGROUND OF THE INVENTION

Light olefins, particularly ethylene and propylene, are important rawmaterials for organic chemical production. The present world demand forethylene for example is about 80 million tons per year, with a majorityof this demand from the polyethylene industry. The preparation ofethylene derivatives, including polyethylene, typically requires ahighly purified ethylene raw material. An ethylene concentration of 99.9mole % is typically required for polyethylene production. Obtainingethylene and propylene at high purity requires difficult separationsfollowing the olefin production process.

One of the most difficult separations that occurs during the olefinproduction process is the removal of non-olefin by-products fromdesirable olefin products. The removal of by-products is desired toachieve high purity olefin products. The removal of these by-productscan be a difficult and expensive task. Extremely low temperatureseparations are generally required to remove these components fromcertain olefin product streams. For this reason, various methods ofreducing the separation requirements have been explored. For example,van Dijk, U.S. Pat. No. 5,811,621, and Kuechler et al. U.S. Pat. No.4,960,643 disclose processes where a less rigorous process of removingmethane by-product is used with a resulting higher concentration ofethylene product. The methane containing by-product is then either usedfor fuel gas or used to make ethylene derivatives with less strictpurity requirements.

Several known process also exist for the production of alcohols from astream containing olefins. Imai, U.S. Pat. No. 4,482,767 discloses amethod of producing lower alcohols from a stream comprising hydrogen,methane, ethane, ethylene, propane, and propylene. The hydration ofethane using several catalysts is further discussed in Frampton, et al.U.S. Pat. No. 4,234,748.

A need exists, therefore, for recovery of olefin, e.g., ethylene andpropylene, during the manufacturing process in order to reduce loss ofolefins which could be used in making olefin derivative products. Inparticular, it is highly desirable to recover olefins which could belost during separation of olefin products obtained from the catalyticconversion of oxygenate components.

SUMMARY OF THE INVENTION

In order to recover olefins which could be lost during separation ofolefin products, this invention provides for hydrating olefins in astream to produce alcohols. The alcohol can then be used to make olefinproducts.

In one embodiment, the invention provides a method of recovering olefinin an oxygenate to olefin reaction process. The method comprisesreacting a stream containing olefin with water in the presence of ahydrating catalyst to produce an alcohol containing stream. The alcoholcontaining stream is combined with an oxygenate feed stream to produce acombined feed stream, and the combined feed stream is contacted with anolefin forming catalyst to form an olefin product stream.

Preferably, the hydrating catalyst is a phosphoric acid catalyst.Preferably, the olefin forming catalyst is a silicoaluminophosphatemolecular sieve catalyst. Preferably, the alcohol containing streamcontains ethanol or propanol. Preferably, the oxygenate feed ismethanol. Preferably, the reaction of a stream containing olefin withwater in the presence of a hydrating catalyst is performed at atemperature of 180° C. to 300° C. and a pressure of 350 psig to 1000psig.

In another embodiment, the invention provides a method of producingolefins from oxygenates. The method comprises mixing an oxygenate feedstream with an alcohol containing stream, with the alcohol containingstream being produced from olefin in the olefin production process. Themixed oxygenate and alcohol feed stream is converted in the presence ofan olefin forming catalyst to form an olefin product stream.

In another embodiment, the invention provides a method of recoveringethylene in an ethylene production process. The method comprisesreacting a stream containing ethylene with water in the presence of ahydrating catalyst to produce an ethanol containing stream. The ethanolfrom the ethanol containing stream is combined with an oxygenate feedstream to produce a combined feed stream, and the combined feed streamis contacted with an ethylene forming catalyst to form an ethyleneproduct stream.

This invention will be better understood by reference to the DetailedDescription of the Invention when taken together with the attachedFIGURE and the appended claims.

BRIEF DESCRIPTION OF THE DRAWING

The FIGURE shows a flow diagram of the process of the invention.

DETAILED DESCRIPTION OF THE INVENTION

During conventional oxygenate to olefin reaction processes non-olefinby-products are formed. These by-products can include hydrogen or lighthydrocarbons, particularly light paraffins such as methane, ethane orpropane. These types of by-products are separated from the moredesirable olefin products. For example, methane and ethane are separatedfrom ethylene, and propane is separated from propylene. However, theseseparations can take multiple steps and require energy intensiveseparation equipment.

This invention makes it possible to use less energy intensive separationsystems to separate olefins from non-olefin by-products, yet maintain ahigh recovery of olefin. This is accomplished converting olefin which isseparated along with the separated by-products to an oxygenate, e.g.,alcohol, and sending the oxygenate back to an oxygenate to olefinsreaction unit.

In the invention, non-olefin by-products are separated from thedesirable olefin products using a non-energy intensive separationsystem. The separated by-products will likely include a substantialquantity of desired olefin product, since the separation is likely to beless rigorous than that conventionally used. In this case, theby-product stream containing the olefin is combined with water in thepresence of a hydrating catalyst. This procedure converts the olefins inthe stream into alcohols. Methane and other undesirable non-olefinby-products are then removed from the alcohol containing stream byconventional techniques.

For example, a non-cryogenic distillation column can be used to condensethe alcohols while the by-products remain in their vapor state. Theby-products can then be removed as a vapor overhead from thedistillation column. The alcohols produced following the hydrationreaction are then combined with an oxygenate feed stream. The combinedfeed stream can then be charged to an olefin reaction process, whichconverts the oxygenates into olefins such as ethylene and propylene.

The removal of by-products in olefin manufacturing conventionallyincorporates the use of a distillation column. The column can include acondenser operating at a temperature of −112° C. to −90° C. (−170° F. to−130° F.) to remove methane and lower boiling point products. Thetemperature reached in the distillation column is typically the lowesttemperature of any separation column in an olefin production plant. Inan ethylene production facility, the distillation column that removesmethane and lower boiling point compounds is most commonly the firstfractionation tower in a product recovery scheme. Additionaldistillation columns can also be used. For example, an additional columncan be used to remove ethane and lighter boiling point compounds, aswell as a column which removes propane and lighter boiling pointcompounds. These columns can be referred to as a demethanizer,deethanizer or depropanizer, respectively. A deethanizer column producesan overhead stream containing hydrogen, methane, acetylene, ethylene,and ethane, and a bottoms product containing higher boiling pointproducts. A depropanizer column produces an overhead stream containingC₃ and lower boiling point products, and a bottoms product containing C₄and higher boiling point products.

In a preferred configuration used for ethylene production, effluent gasfrom a reactor is first compressed, treated, scrubbed, and dried. Mostof the hydrogen can then be removed as a gas after cooling andcondensing the effluent gas at a temperature of about −105° C. andpressure of about 500 psi. The condensed liquid is then sent to ademethanizer column where cryogenic distillation is used to produce anoverhead, which can contain methane and ethylene, and a bottoms productstream which contains ethylene.

The bottoms product from the demethanizer is fed to a deethanizer whereethane and ethylene are separated as an overhead stream from higherboiling point by-products. The overhead stream from the deethanizer isthen sent to a C₂ splitter column to produce an ethylene productoverhead and an ethane containing by-product bottoms stream.

A preferred embodiment of the invention allows for the recovery ofethylene from the by-product streams of the separation columns. This caninclude the ethylene containing overhead stream of a demethanizer columnor any ethylene containing a non-olefin by-product stream.

In one preferred embodiment, a less rigorous methane and hydrogenseparation process is used instead of a conventional demethanizercolumn. Such less rigorous separation processes can include conventionalprocesses such as absorption in a solvent or the use of a demethanizercolumn operating with fewer plates and/or at a higher temperature than aconventional demethanizer column.

Separation of olefins by absorption in a solvent refers to anyconventional process in which olefins such as ethylene can be recoveredby contacting an olefin containing stream with a liquid hydrocarbonsolvent. The solvent preferentially absorbs olefins in the olefinscontaining stream over the residual light by-products.

Solvents suitable for recovering olefins are described in U.S. Pat. No.5,109,143, the solvent and process description of which is expresslyincorporated herein by reference. Preferable solvents include,paraffinic solvents, napthenic solvents, aromatic compounds, and diakylethers. After the solvent has absorbed olefins from the olefincontaining stream, recovery of the olefin product and solvent isaccomplished in a distillation column. The olefin product is recoveredas an overhead product, and the solvent is recovered as a bottom streamwhich can be recycled back to the absorber for further olefin productrecovery.

A preferred separation process will desirably produce two streams from acharge stream containing olefins and non-olefin by-products. One streamis an olefin product stream which contains olefin products with littleto no by-products and the second stream is a by-product stream whichcontains at least a measurable quantity of by-products and preferablyless than 50%, more preferably less than 30%, and most preferably lessthan 10% of the olefin product. The use of these less rigorous processescan result in a higher quantity of olefin in the by-products wastestream, but should not adversely affect the purity of the olefin productstream with the by-products removed. The olefin present in theby-product stream is then recovered by converting the olefin to alcohol.

The invention provides recovery of a wide variety of light olefins. Theolefins that can be recovered include C₂-C₄ branched or linear olefins.Preferably, ethylene and propylene are recovered, most preferablyethylene.

In order to recover the olefin in the methane and olefin containingstream, the olefin in the by-product stream is first hydrated to formalcohol. In a preferred embodiment, ethylene is hydrated to formethanol. The hydration of the olefin can be accomplished either by anindirect route where an intermediate is formed from the olefin prior tothe formation of the alcohol, or a direct route where the olefin isconverted directly into alcohol.

A preferred indirect intermediate route consists of passing an olefingas stream through concentrated sulfuric or phosphoric acid to form anester. Water is then added to the acid ester mixture and heated to formalcohol.

In this invention, it is particularly desirable to use a directhydration process. Conventional direct hydration processes can be usedin this invention. A preferred direct hydration process is liquid phasehydration, which occurs in the presence of a dissolved tungstencontaining catalyst. Two variations of this process are described inU.S. Pat. Nos. 3,758,615 and 3,450,777, the catalyst and processdescriptions of each being expressly incorporated herein by reference. Adirect hydration process using a pelleted tungsten-containing catalystcan also be used as described in U.S. Pat. No. 3,452,106, the catalystand process description being expressly incorporated herein byreference.

Another preferred type of direct hydration process is a mixed phaseprocess in which both gas and liquid phase hydrocarbons are present anda cation exchange resin-type catalyst is employed. Ion exchangecatalysts are synthetic resins possessing a hydrocarbon skeletoncombined with strong mineral acid groups. The use of such a compound inthe direct hydration of an aliphatic olefin is described in U.S. Pat.No. 4,340,769, which is incorporated herein by reference.

The gas phase method is also a preferred embodiment of this invention.Gas phase hydration conventionally employs either a liquid co-feedsystem or an acid loaded on a solid support structure. A preferred acidcatalyst comprises phosphoric acid impregnated on an inert support suchas celite diatomite. A fixed bed catalyst system which comprises asupported phosphoric acid is described at page 195 of the November 1967issue of Hydrocarbon Processing, the description of which is expresslyincorporated herein by reference.

In a preferred gas phase embodiment of this invention, a vaporby-product waste stream containing olefins is combined with water,typically in the form of steam, and fed into a fixed bed hydrationreactor. The ethanol reactor typically operates at a low conversion perpass to minimize the formation of unwanted by-products. Higherconversions are obtained by the use of recycle streams. It is preferredthat the molar ratio of water to entering olefinic hydrocarbon is fromabout 0.5:1 to 40:1. More preferably, this ratio is from about 0.5:1 toabout 20:1. Excess water need not be removed following the hydrationprocess, as some or all of the water can be used as a diluent in theoxygenate to olefin process.

Catalytic hydration may be conducted over a wide range of conditions.Typically, the olefin containing stream is heated in the range of fromabout 180° C. to 300° C. and contacted with the phosphoric acid catalystunder pressure of about 350 psig to 1000 psig.

Direct hydration is an exothermic reaction. The product stream exitingthe reactor comprises a gaseous mixture of steam, alcohols, non-olefinby-products, and unreacted olefins. Following the hydration reaction,the gaseous mixture is charged to a scrubber where the steam andalcohols are condensed and removed from the by-products and unreactedolefins. The stream containing the by-products and unreacted olefins maybe returned to the reactor for a higher olefin to alcohol conversion.

After the hydration process, the alcohols produced are combined with anoxygenate feed stock, which is described in detail below, to produce acombined oxygenate feed stock. The combined oxygenate feed stock is usedto produce olefins. The olefins are recovered from the olefin productstream as described above.

Oxygenates are desirably converted into olefins using a molecular sievecatalyst. In this invention, a preferred molecular sieve catalyst usedto convert the oxygenate feed to olefin is a silicoaluminophosphate(SAPO) molecular sieve catalyst. The molecular sieve comprises athree-dimensional microporous crystal framework structure of [SiO₂],[AlO₂] and [PO₂] corner sharing tetrahedral units. The way Si isincorporated into the structure can be determined by ²⁹Si MAS NMR. SeeBlackwell and Patton, J. Phys. Chem., 92, 3965 (1988). The desired SAPOmolecular sieves will exhibit one or more peaks in the ²⁹Si MAS NMR,with a chemical shift δ(Si) in the range of −88 ppm to −96 ppm and witha combined peak area in that range of at least 20% of the total peakarea of all peaks with a chemical shift δ(Si) in the range of −88 ppm toδ115 ppm, where the δ(Si) chemical shifts refer to externaltetramethylsilane (TMS).

It is preferred that the silicoaluminophosphate molecular sieve used inthis invention have a relatively low Si/Al₂ ratio. In general, the lowerthe Si/Al₂ ratio, the lower the C₁-C₄ saturates selectivity,particularly propane selectivity. A Si/Al₂ ratio of less than 0.65 isdesirable, with a Si/Al₂ ratio of not greater than 0.40 being preferred,and a Si/Al₂ ratio of not greater than 0.32 being particularlypreferred. A Si/Al₂ ratio of not greater than 0.20 is most preferred.

Silicoaluminophosphate molecular sieves are generally classified asbeing microporous materials having 8, 10, or 12 membered ringstructures. These ring structures can have an average pore size rangingfrom about 3.5 angstroms to about 15 angstroms. Preferred are the smallpore SAPO molecular sieves having an average pore size of less thanabout 5 angstroms, preferably an average pore size of about 3.5angstroms to about to 5 angstroms, more preferably from 3.5 angstroms toabout 4.2 angstroms. These pore sizes are typical of molecular sieveshaving 8 membered rings.

In general, silicoaluminophosphate molecular sieves comprise a molecularframework of corner-sharing [SiO₂], [AlO₂], and [PO₂] tetrahedral units.This type of framework is effective in converting various oxygenatesinto olefin products. The [PO₂] tetrahedral units within the frameworkstructure of the molecular sieve of this invention can be provided by avariety of compositions. Examples of these phosphorus-containingcompositions include phosphoric acid, organic phosphates such astriethyl phosphate, and aluminophosphates. The phosphorous-containingcompositions are mixed with reactive silicon and aluminum-containingcompositions under the appropriate conditions to form the molecularsieve.

The [AlO₂] tetrahedral units within the framework structure can beprovided by a variety of compositions. Examples of thesealuminum-containing compositions include aluminum alkoxides such asaluminum isopropoxide, aluminum phosphates, aluminum hydroxide, sodiumaluminate, and pseudoboehmite. The aluminum-containing compositions aremixed with reactive silicon and phosphorus-containing compositions underthe appropriate conditions to form the molecular sieve.

The [SiO₂] tetrahedral units within the framework structure can beprovided by a variety of compositions. Examples of thesesilicon-containing compositions include silica sols and siliciumalkoxides such as tetra ethyl orthosilicate. The silicon-containingcompositions are mixed with reactive aluminum and phosphorus-containingcompositions under the appropriate conditions to form the molecularsieve.

Substituted SAPOs can also be used in this invention. These compoundsare generally known as MeAPSOs or metal-containingsilicoaluminophosphates. The metal can be alkali metal ions (Group IA),alkaline earth metal ions (Group IIA), rare earth ions (Group IIIB,including the lanthanoid elements: lanthanum, cerium, praseodymium,neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium,erbium, thulium, ytterbium and lutetium; and scandium or yttrium) andthe additional transition cations of Groups IVB, VB, VIB, VIIB, VIIIB,and IB.

Preferably, the Me represents atoms such as Zn, Mg, Mn, Co, Ni, Ga, Fe,Ti, Zr, Ge, Sn, and Cr. These atoms can be inserted into the tetrahedralframework through a [MeO₂] tetrahedral unit. The [MeO₂] tetrahedral unitcarries a net electric charge depending on the valence state of themetal substituent. When the metal component has a valence state of +2,+3, +4, +5, or +6, the net electric charge is from −2 to +2.Incorporation of the metal component is typically accomplished addingthe metal component during synthesis of the molecular sieve. However,post-synthesis ion exchange can also be used. In post synthesisexchange, the metal component will introduce cations into ion-exchangepositions at an open surface of the molecular sieve, not into theframework itself

Suitable silicoaluminophosphate molecular sieves include SAPO-5, SAPO-8,SAPO-1, SAPO-16, SAPO-17, SAPO-18, SAPO-20, SAPO-31, SAPO-34, SAPO-35,SAPO-36, SAPO-37, SAPO-40, SAPO-41, SAPO-42, SAPO-44, SAPO-47, SAPO-56,the metal containing forms thereof, and mixtures thereof Preferred areSAPO-17, SAPO-18, SAPO-34, SAPO-35, SAPO-44, and SAPO-47, particularlySAPO-18 and SAPO-34, including the metal containing forms thereof, andmixtures thereof. As used herein, the term mixture is synonymous withcombination and is considered a composition of matter having two or morecomponents in varying proportions, regardless of their physical state.

An aluminophosphate (ALPO) molecular sieve can also be included in thecatalyst composition. Aluminophosphate molecular sieves are crystallinemicroporous oxides which can have an AlPO₄ framework. They can haveadditional elements within the framework, typically have uniform poredimensions ranging from about 3 angstroms to about 10 angstroms, and arecapable of making size selective separations of molecular species. Morethan two dozen structure types have been reported, including zeolitetopological analogues. A more detailed description of the background andsynthesis of aluminophosphates is found in U.S. Pat. No. 4,310,440,which is incorporated herein by reference in its entirety. PreferredALPO structures are ALPO-5, ALPO-11, ALPO-18, ALPO-31, ALPO-34, ALPO-36,ALPO-37, and ALPO-46.

The ALPOs can also include a metal substituent in its framework.Preferably, the metal is selected from the group consisting ofmagnesium, manganese, zinc, cobalt, and mixtures thereof. Thesematerials preferably exhibit adsorption, ion-exchange and/or catalyticproperties similar to aluminosilicate, aluminophosphate and silicaaluminophosphate molecular sieve compositions. Members of this class andtheir preparation are described in U.S. Pat. No. 4,567,029, incorporatedherein by reference in its entirety.

The metal containing ALPOs have a three-dimensional microporous crystalframework structure of MO₂, AlO₂ and PO₂ tetrahedral units. These asmanufactured structures (which contain template prior to calcination)can be represented by empirical chemical composition, on an anhydrousbasis, as:

mR:(M_(x)Al_(y)P_(z))O₂

wherein “R” represents at least one organic templating agent present inthe intracrystalline pore system; “m” represents the moles of “R”present per mole of (M_(X)Al_(y)P_(z))O₂ and has a value of from zero to0.3, the maximum value in each case depending upon the moleculardimensions of the templating agent and the available void volume of thepore system of the particular metal aluminophosphate involved, “x”, “y”,and “z” represent the mole fractions of the metal “M”, (i.e. magnesium,manganese, zinc and cobalt), aluminum and phosphorus, respectively,present as tetrahedral oxides.

The metal containing ALPOs are sometimes referred to by the acronym asMeAPO. Also in those cases where the metal “Me” in the composition ismagnesium, the acronym MAPO is applied to the composition. SimilarlyZAPO, MnAPO and CoAPO are applied to the compositions which containzinc, manganese and cobalt respectively. To identify the variousstructural species which make up each of the subgeneric classes MAPO,ZAPO, CoAPO and MnAPO, each species is assigned a number and isidentified, for example, as ZAPO-5, MAPO-11, CoAPO-34 and so forth.

The silicoaluminophosphate molecular sieves are synthesized byhydrothermal crystallization methods generally known in the art. See,for example, U.S. Pat. Nos. 4,440,871; 4,861,743; 5,096,684; and5,126,308, the methods of making of which are fully incorporated hereinby reference. A reaction mixture is formed by mixing together reactivesilicon, aluminum and phosphorus components, along with at least onetemplate. Generally the mixture is sealed and heated, preferably underautogenous pressure, to a temperature of at least 100° C., preferablyfrom 100° C. to 250° C., until a crystalline product is formed.Formation of the crystalline product can take anywhere from around 2hours to as much as 2 weeks. In some cases, stirring or seeding withcrystalline material will facilitate the formation of the product.

Typically, the molecular sieve product is formed in solution. It can berecovered by standard means, such as by centrifugation or filtration.The product can also be washed, recovered by the same means, and dried.

As a result of the crystallization process, the recovered sieve containswithin its pores at least a portion of the template used in making theinitial reaction mixture. The crystalline structure essentially wrapsaround the template, and the template must be removed so that themolecular sieve can exhibit catalytic activity. Once the template isremoved, the crystalline structure that remains has what is typicallycalled an intracrystalline pore system.

In many cases, depending upon the nature of the final product formed,the template may be too large to be eluted from the intracrystallinepore system. In such a case, the template can be removed by a heattreatment process. For example, the template can be calcined, oressentially combusted, in the presence of an oxygen-containing gas, bycontacting the template-containing sieve in the presence of theoxygen-containing gas and heating at temperatures from 200° C. to 900°C. In some cases, it may be desirable to heat in an environment having alow oxygen concentration. In these cases, however, the result willtypically be a breakdown of the template into a smaller component,rather than by the combustion process. This type of process can be usedfor partial or complete removal of the template from theintracrystalline pore system. In other cases, with smaller templates,complete or partial removal from the sieve can be accomplished byconventional desorption processes such as those used in making standardzeolites.

The reaction mixture can contain one or more templates. Templates arestructure directing or affecting agents, and typically contain nitrogen,phosphorus, oxygen, carbon, hydrogen or a combination thereof, and canalso contain at least one alkyl or aryl group, with 1 to 8 carbons beingpresent in the alkyl or aryl group. Mixtures of two or more templatescan produce mixtures of different sieves or predominantly one sievewhere one template is more strongly directing than another.

Representative templates include tetraethyl ammonium salts,cyclopentylamine, aminomethyl cyclohexane, piperidine, triethylamine,cyclohexylamine, tri-ethyl hydroxyethylamine, morpholine, dipropylamine(DPA), pyridine, isopropylamine and combinations thereof. Preferredtemplates are triethylamine, cyclohexylamine, piperidine, pyridine,isopropylamine, tetraethyl ammonium salts, dipropylamine, and mixturesthereof. The tetraethylammonium salts include tetraethyl ammoniumhydroxide (TEAOH), tetraethyl ammonium phosphate, tetraethyl ammoniumfluoride, tetraethyl ammonium bromide, tetraethyl ammonium chloride,tetraethyl ammonium acetate. Preferred tetraethyl ammonium salts aretetraethyl ammonium hydroxide and tetraethyl ammonium phosphate.

The SAPO molecular sieve structure can be effectively controlled usingcombinations of templates. For example, in a particularly preferredembodiment, the SAPO molecular sieve is manufactured using a templatecombination of TEAOH and dipropylamine. This combination results in aparticularly desirable SAPO structure for the conversion of oxygenates,particularly methanol and dimethyl ether, to light olefins such asethylene and propylene.

The silicoaluminophosphate molecular sieve is typically admixed (i.e.,blended) with other materials. When blended, the resulting compositionis typically referred to as a SAPO catalyst, with the catalystcomprising the SAPO molecular sieve.

Materials which can be blended with the molecular sieve can be variousinert or catalytically active materials, or various binder materials.These materials include compositions such as kaolin and other clays,various forms of rare earth metals, metal oxides, other non-zeolitecatalyst components, zeolite catalyst components, alumina or aluminasol, titania, zirconia, magnesia, thoria, beryllia, quartz, silica orsilica or silica sol, and mixtures thereof. These components are alsoeffective in reducing, inter alia, overall catalyst cost, acting as athermal sink to assist in heat shielding the catalyst duringregeneration, densifying the catalyst and increasing catalyst strength.It is particularly desirable that the inert materials that are used inthe catalyst to act as a thermal sink have a heat capacity of from about0.05 cal/g-°C. to about 1 cal/g-°C., more preferably from about 0.1cal/g-°C. to about 0.8 cal/g-°C., most preferably from about 0.1cal/g-°C. to about 0.5 cal/g-°C.

Additional molecular sieve materials can be included as a part of theSAPO catalyst composition or they can be used as separate molecularsieve catalysts in admixture with the SAPO catalyst if desired.Structural types of small pore molecular sieves that are suitable foruse in this invention include AEI, AFT, APC, ATN, ATT, ATV, AWW, BIK,CAS, CHA, CHI, DAC, DDR, EDI, ERI, GOO, KFI, LEV, LOV, LTA, MON, PAU,PHI, RHO, ROG, THO, and substituted forms thereof. Structural types ofmedium pore molecular sieves that are suitable for use in this inventioninclude MFI, MEL, MTW, EUO, MTT, HEU, FER, AFO, AEL, TON, andsubstituted forms thereof. Preferred molecular sieves which can becombined with a silicoaluminophosphate catalyst include ZSM-5, ZSM-34,erionite, and chabazite.

The catalyst composition preferably comprises about 1% to about 99%,more preferably about 5% to about 90%, and most preferably about 10% toabout 80%, by weight of molecular sieve. It is also preferred that thecatalyst composition have a particle size of about 20 μ to 3,000 μ morepreferably about 30 μ to 200 μ most preferably about 50 μ to 150 μ.

The catalyst can be subjected to a variety of treatments to achieve thedesired physical and chemical characteristics. Such treatments include,but are not necessarily limited to hydrothermal treatment, calcination,acid treatment, base treatment, milling, ball milling, grinding, spraydrying, and combinations thereof.

In this invention, the feed containing oxygenates, preferably methanoland ethanol, and optionally a diluent or a hydrocarbon added separatelyor mixed with the oxygenate, is contacted with a catalyst, preferably aSAPO molecular sieve catalyst, in a reaction zone or volume. The volumein which such contact takes place is herein termed the “reactor,” whichmay be a part of a “reactor apparatus” or “reaction system.” Anotherpart of the reaction system may be a “regenerator,” which comprises avolume wherein carbonaceous deposits (or coke) on the catalyst resultingfrom the olefin conversion reaction are removed by contacting thecatalyst with regeneration medium.

The oxygenate feedstock of this invention comprises at least one organiccompound which contains at least one oxygen atom, such as aliphaticalcohols, ethers, carbonyl compounds (aldehydes, ketones, carboxylicacids, carbonates, esters and the like). When the oxygenate isan-alcohol, the alcohol can include an aliphatic moiety having from 1 to10 carbon atoms, more preferably from 1 to 4 carbon atoms.Representative alcohols include but are not necessarily limited to lowerstraight and branched chain aliphatic alcohols and their unsaturatedcounterparts. Examples of suitable oxygenate compounds include, but arenot limited to: methanol; ethanol; n-propanol; isopropanol; C₄-C₂₀alcohols; methyl ethyl ether, dimethyl ether; diethyl ether;di-isopropyl ether; formaldehyde; dimethyl carbonate; dimethyl ketone;acetic acid; and mixtures thereof. Preferred oxygenate compounds aremethanol, dimethyl ether, or a mixture thereof. The alcohols produced inthis invention are suitable oxygenates and can be combined with anotherfeed containing suitable oxygenates.

The method of making the preferred olefin product in this invention caninclude the additional step of making these compositions fromhydrocarbons such as oil, coal, tar sand, shale, biomass and naturalgas. Methods for making the compositions are known in the art. Thesemethods include fermentation to alcohol or ether, making synthesis gas,then converting the synthesis gas to alcohol or ether. Synthesis gas canbe produced by known processes such as steam reforming, autothermalreforming and partial oxidization.

One or more inert diluents may be present in the feedstock, for example,in an amount of from 1 to 99 molar percent, based on the total number ofmoles of all feed and diluent components fed to the reaction zone (orcatalyst). As defined herein, diluents are compositions which areessentially non-reactive across a molecular sieve catalyst, andprimarily function to make the oxygenates in the feedstock lessconcentrated. Typical diluents include, but are not necessarily limitedto helium, argon, nitrogen, carbon monoxide, carbon dioxide, water,essentially non-reactive paraffins (especially the alkanes such asmethane, ethane, and propane), essentially non-reactive alkylenes,essentially non-reactive aromatic compounds, and mixtures thereof. Thepreferred diluents are water and nitrogen. Water can be injected ineither liquid or vapor form.

Hydrocarbons can also be included as part of the feedstock, i.e., asco-feed. As defined herein, hydrocarbons included with the feedstock arehydrocarbon compositions which are converted to another chemicalarrangement when contacted with molecular sieve catalyst. Thesehydrocarbons can include olefins, reactive paraffins, reactivealkylaromatics, reactive aromatics or mixtures thereof. Preferredhydrocarbon co-feeds include, propylene, butylene, pentylene, C₄ ⁺hydrocarbon mixtures, C₅ ⁺ hydrocarbon mixtures, and mixtures thereof.More preferred as co-feeds are a C₄ ⁺ hydrocarbon mixtures, with themost preferred being C₄ ⁺ hydrocarbon mixtures which are obtained fromseparation and recycle of reactor product.

In the process of this invention, coked catalyst can be regenerated bycontacting the coked catalyst with a regeneration medium to remove allor part of the coke deposits. This regeneration can occur periodicallywithin the reactor by ceasing the flow of feed to the reactor,introducing a regeneration medium, ceasing flow of the regenerationmedium, and then reintroducing the feed to the fully or partiallyregenerated catalyst. Regeneration may also occur periodically orcontinuously outside the reactor by removing a portion of thedeactivated catalyst to a separate regenerator, regenerating the cokedcatalyst in the regenerator, and subsequently reintroducing theregenerated catalyst to the reactor. Regeneration can occur at times andconditions appropriate to maintain a desired level of coke on the entirecatalyst within the reactor.

Catalyst that has been contacted with feed in a reactor is definedherein as “feedstock exposed.” Feedstock exposed catalyst will provideolefin conversion reaction products having substantially lower propaneand coke content than a catalyst which is fresh and regenerated. Acatalyst will typically provide lower amounts of propane as it isexposed to more feed, either through increasing time at a given feedrate or increasing feed rate over a given time.

At any given instant in time, some of the catalyst in the reactor willbe fresh, some regenerated, and some coked or partially coked as aresult of having not yet been regenerated. Therefore, various portionsof the catalyst in the reactor will have been feedstock exposed fordifferent periods of time. Since the rate at which feed flows to thereactor can vary, the amount of feed to which various portions of thecatalyst can also vary. To account for this variation, the “averagecatalyst feedstock exposure index (ACFE index)” is used toquantitatively define the extent to which the entire catalyst in thereactor has been feedstock exposed.

As used herein, ACFE index is the total weight of feed divided by thetotal weight of molecular sieve (i.e., excluding binder, inerts, etc.,of the catalyst composition) sent to the reactor. The measurement shouldbe made over an equivalent time interval, and the time interval shouldbe long enough to smooth out fluctuations in catalyst or feedstock ratesaccording to the reactor and regeneration process step selected to allowthe system to be viewed as essentially continuous. In the case ofreactor systems with periodic regenerations, this can range from hoursup to days or longer. In the case of reactor systems with substantiallyconstant regeneration, minutes or hours may be sufficient.

Flow rate of catalyst can be measured in a variety of ways. In thedesign of the equipment used to carry the catalyst between the reactorand regenerator, the catalyst flow rate can be determined given the cokeproduction rate in the reactor, the average coke level on catalystleaving the reactor, and the average coke level on catalyst leaving theregenerator. In an operating unit with continuous catalyst flow, avariety of measurement techniques can be used. Many such techniques aredescribed, for example, by Michel Louge, “Experimental Techniques,”Circulating Fluidized Beds, Grace, Avidan, & Knowlton, eds., Blackie,1997 (336-337), the descriptions of which are expressly incorporatedherein by reference.

In a preferred embodiment of this invention, only the molecular sieve inthe catalyst sent to the reactor may be used in the determination ofACFE index. The catalyst sent to the reactor, however, can be eitherfresh or regenerated or a combination of both. Molecular sieve which maybe recirculated to and from the reactor within the reactor apparatus(i.e., via ducts, pipes or annular regions), and which has not beenregenerated or does not contain fresh catalyst, is not to be used in thedetermination of ACFE index.

In a preferred embodiment of this invention, a feed containing theoxygenates, and optionally a hydrocarbon, either separately or mixedwith the oxygenates, is contacted with a catalyst containing a SAPOmolecular sieve at process conditions effective to produce olefins in areactor where the catalyst has an ACFE index of at least about 1.0,preferably at least 1.5. An ACFE index of about 1.0 to 20 is effective,with about 1.5 to 15 being desirable. An ACFE index of about 2 to 12 isparticularly preferred.

Any standard reactor system can be used, including fixed bed, fluid bedor moving bed systems. Preferred reactors are co-current riser reactorsand short contact time, countercurrent free-fall reactors. Desirably,the reactor is one in which the oxygenates can be contacted with amolecular sieve catalyst at a weight hourly space velocity (WHSV) of atleast about 1 hr⁻¹, preferably of from about 1 hr⁻¹ to about 1000 hr⁻¹,more preferably of from about 20 hr⁻¹ to about 1000 hr⁻¹, and mostpreferably of from about 20 hr⁻¹ to about 500 hr⁻¹. WHSV is definedherein as the weight of oxygenate, and hydrocarbon which may optionallybe in the feed, per hour per weight of the molecular sieve content ofthe catalyst. Because the catalyst or the combined oxygenate feed stockmay contain other materials which act as inerts or diluents, the WHSV iscalculated on the weight basis of the oxygenate feed, and anyhydrocarbon which may be present, and the molecular sieve contained inthe catalyst.

Preferably, the combined oxygenate feed is contacted with the catalystwhen the oxygenate is in a vapor phase. Alternately, the process may becarried out in a liquid or a mixed vapor/liquid phase. When the processis carried out in a liquid phase or a mixed vapor/liquid phase,different conversions and selectivities of feed-to-product may resultdepending upon the catalyst and reaction conditions.

The process can generally be carried out at a wide range oftemperatures. An effective operating temperature range can be from about200° C. to 700° C., preferably from about 300° C. to 600° C., morepreferably from about 350° C. to 550° C. At the lower end of thetemperature range, the formation of the desired olefin products maybecome markedly slow. At the upper end of the temperature range, theprocess may not form an optimum amount of product.

It is highly desirable to operate at a temperature of at least 300° C.and a Temperature Corrected Normalized Methane Sensitivity (TCNMS) ofless than about 0.016. It is particularly preferred that the reactionconditions for making olefin from oxygenates comprise a WHSV of at leastabout 20 hr⁻¹ producing olefins and a TCNMS of less than about 0.016.

As used herein, TCNMS is defined as the Normalized Methane Selectivity(NMS) when the temperature is less than 400° C. The NMS is defined asthe methane product yield divided by the ethylene product yield whereineach yield is measured on, or is converted to, a weight % basis. Whenthe temperature is 400° C. or greater, the TCNMS is defined by thefollowing equation, in which T is the average temperature within thereactor in ° C.:${TCNMS} = \frac{NMS}{1 + \left( {\left( {\left( {T - 400} \right)/400} \right) \times 14.84} \right)}$

The pressure also may vary over a wide range, including autogenouspressures. Effective pressures may be in, but are not necessarilylimited to, oxygenate partial pressures at least 1 psia, preferably atleast 5 psia. The process is particularly effective at higher oxygenatepartial pressures, such as an oxygenate partial pressure of greater than20 psia. Preferably, the oxygenate partial pressure is at least about 25psia, more preferably at least about 30 psia. For practical designpurposes it is desirable to operate at a methanol partial pressure ofnot greater than about 500 psia, preferably not greater than about 400psia, most preferably not greater than about 300 psia.

The conversion of oxygenates to produce light olefins may be carried outin a variety of catalytic reactors. Reactor types include conventionalreactors such as fixed bed reactors, fluid bed reactors, and riserreactors. Preferred reactors are riser reactors. Additionally,countercurrent free fall reactors may be used in the conversion processof the present invention. Countercurrent free fall reactors aredescribed, for example, in U.S. Pat. No. 4,068,136, which isincorporated by reference herein in its entirety.

In a preferred embodiment of the continuous operation, only a portion ofthe catalyst is removed from the reactor and sent to the regenerator toremove the accumulated coke deposits that result during the catalyticreaction. In the regenerator, the catalyst is contacted with aregeneration medium containing oxygen or other oxidants. Examples ofother oxidants include O₃, SO₃, N₂, NO, NO₂, N₂O₅, and mixtures thereof.It is preferred to supply O₂ in the form of air. The air can be dilutedwith nitrogen, CO₂, or flue gas, and steam may be added. Desirably, theO₂ concentration in the regenerator is reduced to a controlled level tominimize overheating or the creation of hot spots in the spent ordeactivated catalyst. The deactivated catalyst also may be regeneratedreductively with H₂, CO, mixtures thereof, or other suitable reducingagents. A combination of oxidative regeneration and reductiveregeneration can also be employed.

In essence, the coke deposits are removed from the catalyst during theregeneration process, forming a regenerated catalyst. The regeneratedcatalyst is then returned to the reactor for further contact with feed.Typical regeneration temperatures are from 250° C. to 700° C., desirably350° C. to 700° C. Preferably, regeneration is carried out at atemperature of 450° C. to 700° C.

It is desirable to strip at least some of the volatile organiccomponents which may be adsorbed onto the catalyst or located within itsmicroporous structure prior to entering the regenerator. This can beaccomplished by-passing a stripping gas over the catalyst in a stripperor stripping chamber, which can be located within the reactor or in aseparate vessel. The stripping gas can be any substantially inert mediumthat is commonly used. Examples of stripping gas are steam, nitrogen,helium, argon, methane, CO₂, CO, flue gas, and hydrogen.

It may be desirable to cool at least a portion of the regeneratedcatalyst to a lower temperature before it is sent back to the reactor. Aheat exchanger located externally to the regenerator may be used toremove some heat from the catalyst after it has been withdrawn from theregenerator. When the regenerated catalyst is cooled, it is desirable tocool it to a temperature which is from about 200° C. higher to about200° C. lower than the temperature of the catalyst withdrawn from thereactor. More desirably, it is cooled to a temperature from about 10° C.to 200° C. lower than the temperature of the catalyst withdrawn from thereactor. This cooled catalyst then may be returned to either someportion of the reactor, the regenerator, or both. When the regeneratedcatalyst from the regenerator is returned to the reactor, it may bereturned to the reactor's catalyst disengaging zone, the reaction zone,and/or the inlet zone. Introducing the cooled catalyst into the reactoror regenerator serves to reduce the average temperature in the reactoror regenerator.

In one embodiment, the reactor and regenerator are configured such thatthe feed contacts the regenerated catalyst before it is returned to thereactor. In an alternative embodiment, the reactor and regenerator areconfigured such that the feed contacts the regenerated catalyst after itis returned to the reactor. In yet another embodiment, the feed streamcan be split such that feed contacts regenerated catalyst before it isreturned to the reactor and after it has been returned to the reactor.

It is preferred that the catalyst within the reactor have an averagelevel of coke effective for selectivity to ethylene and/or propylene.Preferably, the average coke level on the catalyst will be from about 2wt. % to about 30 wt. %, more preferably from about 2 wt. % to about 20wt. %. In order to maintain this average level of coke on catalyst, theentire volume of catalyst can be partially regenerated under conditionseffective to maintain the desired coke content on catalyst. It ispreferred, however, to recycle only a portion of the coked catalyst forfeed contact without regenerating. This recycle can be performed eitherinternal or external to the reactor. The portion of coked catalyst to beregenerated is preferably regenerated under conditions effective toobtain a regenerated catalyst having a coke content of less than 2 wt.%, preferably less than 1.5 wt. %, and most preferably less than 1.0 wt.%.

In order to make up for any catalyst loss during the regeneration orreaction process, fresh catalyst can be added. Preferably, the freshcatalyst is added to the regenerated catalyst after it is removed fromthe regenerator, and then both are added to the reactor. However, thefresh catalyst can be added to the reactor independently of theregenerated catalyst. Any amount of fresh catalyst can be added, but itis preferred that an ACFE index of at least 1.5 be maintained.

One skilled in the art will also appreciate that the olefins produced bythe oxygenate-to-olefin conversion reaction of the present invention canbe polymerized to form polyolefins, particularly polyethylene andpolypropylene. Processes for forming polyolefins from olefins are knownin the art. Catalytic processes are preferred. Particularly preferredare metallocene, Ziegler/Natta and acid catalytic systems. See, forexample, U.S. Pat. Nos. 3,258,455; 3,305,538; 3,364,190; 5,892,079;4,659,685; 4,076,698; 3,645,992; 4,302,565; and 4,243,691, the catalystand process descriptions of each being expressly incorporated herein byreference. In general, these methods involve contacting the olefinproduct with a polyolefin-forming catalyst at a pressure and temperatureeffective to form the polyolefin product.

A preferred polyolefin-forming catalyst is a metallocene catalyst. Thepreferred temperature range of operation is from 50° C. to 240° C. andthe reaction can be carried out at low, medium or high pressure, beinganywhere within the range of about 1 bar to 200 bars. For processescarried out in solution, an inert diluent can be used, and the preferredoperating pressure range is from 10 bars to 150 bars, with a preferredtemperature of 120° C. to 230° C. For gas phase processes, it ispreferred that the temperature generally be from 60° C. to 160° C., andthat the operating pressure be from 5 bars to 50 bars.

In addition to polyolefins, numerous other olefin derivatives may beformed from the olefins recovered therefrom. These include, but are notlimited to, aldehydes, alcohols, acetic acid, linear alpha olefins,vinyl acetate, ethylene dicholoride and vinyl chloride, ethylbenzene,ethylene oxide, cumene, isopropyl alcohol, acrolein, allyl chloride,propylene oxide, acrylic acid, ethylene-propylene rubbers, andacrylonitrile, and trimers and dimers of ethylene, propylene orbutylenes. The methods of manufacturing these derivatives are well knownin the art, and therefore, are not discussed herein.

A preferred embodiment of the invention is shown in the FIGURE. In theFIGURE, a methanol containing feed stream 1, along with an ethanolcontaining feed stream 13, is fed into an olefin-producing reactor 2.The reactor 2 contains a catalyst that converts the ethanol and methanolinto olefin containing stream 3. Olefin containing stream 3 is then sentto recovery section 4. The recovery section can include conventionalseparation systems that produce a purified ethylene stream 5, a purifiedpropylene containing stream 6, and a by-products stream 7. Includedwithin the recovery section is a separation system for removing methaneand lower boiling point compounds from the purified ethylene stream 5.The separation system produces a stream 8, which contains methane andlower boiling point compounds along with an amount of ethylene as wellas ethane. Stream 8 is feed into an alcohol formation zone where waterstream 10 and an acid catalyst 11 are combined to convert ethylene instream 8 into ethanol. The methane and other non-olefin by-products areremoved as stream 12. The ethanol-containing stream 13 is then returnedto olefin producing reactor 2.

In an alternative embodiment, separation equipment could be used inrecovery section 4 to further purify propylene. For example, propanecould be separated from the propylene using a distillation system. If aless rigorous separation system is used, significant quantities ofpropylene could be removed along with the propane. In this case, thepropylene that is removed along with the propane can be sent to thealcohol formation zone and converted to propanol. The propanol can thenbe sent back through line 13 to the reactor 2.

Having now fully described this invention, it will be appreciated bythose skilled in the art that the invention can be performed within awide range of parameters within what is claimed, without departing fromthe spirit and scope of the invention.

What is claimed is:
 1. A method of recovering olefin from a by-productstream in an oxygenate to olefin reaction process to form additionalolefin product, comprising: contacting oxygenate with a molecular sievecatalyst to form an olefin product stream and a by-product stream;separating the olefin product stream from the by-product stream;hydrating olefin in the by-product stream to produce an alcoholcontaining stream; and contacting alcohol in the alcohol containingstream with a molecular sieve catalyst to form additional olefinproduct.
 2. The method of claim 1, wherein olefin is recovered from theolefin product stream.
 3. The method of claim 1, wherein the olefin inthe by-product stream is hydrated by contacting with a phosphoric acidcatalyst.
 4. The method of claim 1, wherein the molecular sieve catalystis a silicoaluminophosphate molecular sieve catalyst.
 5. The method ofclaim 1, wherein the alcohol in the alcohol containing stream is ethanolor propanol.
 6. The method of claim 1, wherein the oxygenate ismethanol.
 7. The method of claim 1, wherein the hydrating is performedat a temperature of 180° C. to 300° C.
 8. The method of claim 1, whereinthe hydrating is performed at a pressure of 350 psig to 1000 psig.
 9. Amethod of recovering ethylene from a by-product stream in an ethyleneproduction process to form additional ethylene product, comprising;contacting oxygenate with a molecular sieve catalyst to form an ethyleneproduct stream and a by-product stream; separating the ethylene productstream from the by-product stream; hydrating ethylene in the by-productstream to produce an ethanol containing stream; and contacting ethanolin the ethanol containing stream with a molecular sieve catalyst to formadditional ethylene product.
 10. The method of claim 9, wherein theolefin in the by-product stream is hydrated by contacting with aphosphoric acid catalyst.
 11. The method of claim 9, wherein themolecular sieve catalyst is a silicoaluminophosphate molecular sievecatalyst.
 12. The method of claim 9 wherein the ethylene is recoveredfrom the ethylene product stream.
 13. The method of claim 9, wherein theoxygenate is methanol.
 14. The method of claim 9, wherein the hydratingis performed at a temperature of 180° C. to 300° C. and a pressure of350 psig to 1000 psig.